Morton suffered their 10th successive league defeat after Dumbarton secured a 2-0 win at the Bet Butler Stadium.
The visitors were fortunate to end the game with 11 men too after Tomas Peciar could have been sent off for a last-man challenge on Bryan Prunty after 17 minutes.
Both teams had first-half goals disallowed for offside. Fouad Bachirou was denied giving Morton the lead after 32 minutes, while Mark McLaughlin had his effort chalked off for the Sons.
Dumbarton were awarded a penalty in injury time at the end of the first half when Chris Turner's strike from 25 yards hit Reece Hands on the arm. Bryan Prunty converted the spot-kick into the bottom-left corner, sending goalkeeper Nicolas Caraux the wrong way.
And the Sons wrapped up victory nine minutes from time. Colin Nish's effort was initially blocked, but the striker chipped the rebound across goal for substitute Chris Kane to head home from just six yards out on his debut.